1. Field of the Invention
The present invention relates to a processing method and apparatus for a plasma used for frequent use in processing of a semiconductor wafer, in manufacturing an integrated circuit, or a plasma apparatus for performing a plasma treatment.
2. Description of the Related Art
A treatment method using a plasma has heretofore been broadly used because the method is very useful in various semiconductor manufacturing processes such as etching, resist removal, and vapor deposition. For inductively coupled plasmas for generally frequent use, such as TCP and ICP, a predetermined gas is passed through a chamber sealed by a surrounding member including a dielectric window member, and an RF current, for example, of 13.56 MHz is passed through an RF induction coil disposed in the vicinity of the outside of the window member. Thereby, an electromagnetic field is generated in the chamber, and an electron is accelerated and collides against a molecule so that an ion and radical are generated.
This ion and radical have a very high reactivity, and are frequently used in treatment processes such as plasma etching and plasma deposition. The inductively coupled plasma has advantages such as that a high-density plasma can be generated, a large wafer area can be handled, and the induction coil does not contact the plasma without polluting any metal. Therefore, the plasma still fulfils a most important function in a semiconductor manufacturing field.
However, electric and magnetic fields are simultaneously generated in the inductively coupled plasma, and a drift is generated in the electron. This brings the plasma into an unstable state, and a phenomenon called a plasma instability occurs. This is a problem inherent in this field. Moreover, when a reflected wave (reflection power) indicating a value not less than a predetermined value is generated because of the plasma instability, a manufactured product is variously adversely affected. Here, problems caused by the plasma instability in manufacturing semiconductor products such as an integrated circuit will concretely be described. The problems include instability of a manufacturing process, damage to the product, decreased yield, drop of operation ratio, differences generated among manufacturing apparatus, and the like.
Examples of conditions under which the plasma instability is generated roughly include several factors such as a process gas type, gas pressure, and RF power. Even if optimum process conditions are established, the optimum process conditions have to be sometimes changed because of the plasma instability (reflection power generation).
Moreover, the plasma instability has not been fundamentally solved for a long time since observed, and an effective method of suppressing the plasma instability has not yet been obtained.